1. Field of the Invention
This invention relates to an inkjet printing apparatus including a plurality of inkjet heads.
2. Description of the Prior Art
Conventionally, in an inkjet printing apparatus including inkjet heads each having numerous inkjet nozzles, cleaning by suction (suction purge) is carried out for the inkjet heads in order to eliminate a printing failure called missing nozzle due to clogging of part of the inkjet nozzles.
The inkjet recording apparatus described in Japanese Unexamined Patent Publication No. 2008-213216, for example, includes caps for individually covering discharge opening groups (inkjet heads), a pump for drawing ink by suction from ink discharge openings (inkjet nozzles) into the caps, and switch valves respectively mounted on connecting paths connecting the individual caps to the pump. In this inkjet recording apparatus, by selectively opening the switch valves mounted on the connecting paths communicating with the respective caps of the discharge opening groups (inkjet heads), for example, only the cap covering an inkjet head which includes an inkjet nozzle failing to discharge ink can be connected to the pump, to undergo a suction purge for individually sucking the ink.
An inkjet printing apparatus has also been proposed, which includes a cleaning mechanism capable of a general suction which carries out suction for a plurality of inkjet heads collectively, and an individual suction for only one inkjet head (see International Publication No. 2007/058139). This cleaning mechanism is formed of a cap for individual suction, which is one of caps for individually covering a plurality of inkjet heads, and which may be connected to a pump through a tube, the other caps being connected to the pump through a tube branched to be connected to the plurality of caps, a first switch valve for switching sucking operation of the plurality of caps at the same time, and a second switch valve for switching sucking operation of only the cap for individual suction. When carrying out the general suction, all the plurality of inkjet heads are covered with the caps, and the first and second switch valves are opened. When carrying out the individual suction, only one inkjet head is covered with the cap for individual suction, the first switch valve is closed, and the second switch valve is opened, thereby allowing the desired inkjet head to undergo the suction.
However, with the apparatus described in Japanese Unexamined Patent Publication No. 2008-213216, it is necessary to arrange numerous electromagnetic switch valves corresponding to the number of caps, which poses a problem of enlarging the apparatus and increasing production cost. Driving the numerous electromagnetic switch valves also poses a problem of increasing power consumption, and thus increasing running cost.
On the other hand, the apparatus described in International Publication No. 2007/058139 carries out a cleaning operation for each inkjet unit having a plurality of inkjet heads juxtaposed in one direction. Therefore, when an individual suction of the inkjet heads is carried out, depending on the position in an inkjet unit of the inkjet head requiring suction, an extended time is consumed in moving the inkjet unit for positioning the inkjet head relative to the cap for individual suction. This poses a problem of taking a long time in cleaning the inkjet head.